This invention concerns a railway truck and a flexible roller bearing adapter assembly which provides fit-up between a bearing journal and a side frame in a conventional three-piece railway truck such that the wheelsets can move independently with respect to the side frames as is required to achieve proper wheelset tracking on both curved and tangent track. Various benefits are realized, including reduced flange-to-rail contact and reduced sliding at the interface between the wheel and rail running surfaces.
The invention contemplates a bearing adapter assembly which includes elastomeric elements having a form or geometry that provides for three dimensional support of the side frame pedestals on the bearing journals in a manner that permits necessary and controlled bearing journal translation longitudinally of the side frames in the pedestal opening through differential deformation of the elastomer, including compression thereof. The invention further provides continuously wear-compensated longitudinal and lateral bearing adapter-to-pedestal constraint.
A conventional three piece railway truck is comprised of a pair of laterally spaced side frames which are supported on a pair of longitudinally spaced wheelsets, and an elongated bolster which extends between the spaced side frames and is supported thereon by springs. Practitioners in the art have continuously sought to improve the performance of such trucks in an effort to realize improved truck component service life, reduced rail wear, improved fuel economy and operating reliability, increased safety, and other benefits which can result in overall enhancement of railway rolling stock performance.
As usually furnished commercially, modern railway truck wheelset roller bearings permit only very limited wheelset movement with respect to the side frames. For example, such bearings permit no substantial lateral freedom for the wheelsets to move laterally with respect to the truck side frames. More specifically, it is well known that when a conical wheelset of a conventional truck is displaced laterally on the rails, the wheels roll on unequal radii. The wheel which rolls on the larger radius moves ahead of the other wheel thus steering the wheelset from the laterally displaced position toward the center position, where the wheels roll on equal radii. However, as the wheelset continues on its preferred path, it passes the equilibrium or centered position and moves to a laterally displaced position on the opposite side of center, from which the effect of the wheels rolling on unequal radii again steers the wheelset back toward the centered position. The wheelset thus continuously rolls along a substantially sinusoidal path when there is no sliding at the rail-wheel interface. In order to follow such a sinusoidal path the wheelsets move with respect to the side frames to either a trapezoidal geometry as in radial steering, or a parallelogram geometry such as commonly occurs when the truck warps.
Due to the lack of lateral freedom in the roller bearings, the entire truck will tend to follow such a sinusoidal path. At higher speeds the motion of an empty car body will tend to couple with lateral truck oscillations to produce violent cyclical lateral car body accelerations, commonly known as hunting, which can result in accelerated wear of rail car components and rails as well as other undesirable consequences including lading damage.
Conventional prior art trucks also permit the wheelset bearing journals only very limited longitudinal and rotational freedom in the horizontal plane with respect to the side frame pedestals due to bearing adapter-to-side frame horizontal friction and restricted motion limits. As a result, the wheelsets of prior art trucks have insufficient longitudinal freedom at the side frame pedestals to steer to a radial alignment when traversing curved track. Consequently, the wheelsets tend to slide on the rails when negotiating curved track. The inability of the wheelsets of such trucks to steer thus results in severe frictional rubbing contact between the wheel flanges and the rails, and accelerated flange and rail head wear on shorter radius curves. Under such conditions, fuel economy also suffers as a great deal of energy is dissipated by such rubbing contact. More severe flange rubbing also may create a tendency for the wheel to climb the rail thus precipitating a derailment. Furthermore, improper wheelset tracking on curves may also cause or aggravate track misalignment.
The variable restraining friction and unpredictable motion limits between the bearing journal adapter and the side frame pedestal in conventional trucks also results in tracking energy losses on tangent track. When the wheelsets of a truck cannot achieve a free rolling alignment on tangent track due to asymmetrical tread wear and/or journal-to-pedestal restraint, the resulting wheel tread slip and/or flange rubbing causes increased wheelset rolling energy dissipation.
The art has contemplated trucks which include resilient wheelset journal suspension to provide greater freedom of relative motion than in trucks such as those characterized above. For example, steering trucks are known which use articulating techniques such as mechanical linkage systems, usually in the form of steering arms, for the simultaneous control of both wheelsets in the truck. Nearly all such articulated steering trucks and other known truck designs require resilient journal suspension at the side frame pedestals. However, to be effective the resilient suspension must be sufficiently elastic in horizontal shear to permit the bearing journal to move longitudinally in the pedestal for steering, and must also be sufficiently stiff in the lateral direction so as not to reduce the composite lateral car body-to-truck spring constant and thereby encourage low speed empty car hunting. As a result of these conflicting requirements, known resilient journal suspensions often have yielded either unsatisfactory control at lower empty car speeds or a limited or ineffective steering capability. For example, many prior resilient journal suspensions, commonly the "sandwich" configurations in which elastomer is sandwiched or laminated in alternate layers with a rigid substrate such as a steel plate, the available lateral and longitudinal restraint are identical and therefore unable to accommodate such conflicting requirements as those specified above.
The prior art has also contemplated the use of resilient elastomers in conjunction with the bearing adapters of railway truck wheelsets for load cushioning or shock absorption. Some such prior art pertains to trucks with so-called plane bearings. Patents of interest include U.S. Pat. Nos. 149,284, 301,510, 1,222,698, 1,904,007, 2,234,413, 2,239,646, 2,842,409, 2,957,733, 3,033,617, 3,098,682, 3,222,111, 4,044,689, and 2,207,848. The above cited patents are not generally concerned with journal-to-side frame flexibility for the purpose of wheelset steering.